1. Field of the Invention
The present invention relates to three dimensional graphic accelerators, and more particularly to a three dimensional parallax drawing system for use with virtual reality systems.
2. Description of the Related Art
Most modern graphic boards have graphic accelerators which provide the ability to quickly move data to video memory from other places in the computer. Graphic accelerators have been improved for use in three-dimensional games or graphics as well as virtual reality. In order to implement the 3-D graphics, well known texture mapping, perspective projection, shading, fog and depth cueing techniques are widely used. Texture mapping allows the graphic accelerator to calculate the memory address of the desired 3-D image to read out the texture data stored in the video memory and again write into the frame buffer. These techniques provide two-dimensional images with a sense of perspective; however, the 3-D image produced by conventional graphic accelerators is somewhat different from what is seen by human eyes in the real world. The human eyes perceives how far away an object is by using parallax. FIG. 1 shows the binocular disparity relative to a hexahedral object. Assuming a view plane 10 in front of the human eyes, a left eye's view 20 and a right eye's view 30 are formed in the view plane 10 and reach the retinas of two eyes LE and RE. The left eye's view 20 is different in shape from the right eye's view 30 due to the distance between the two eyes. This binocular disparity results in a perception of how far or near the object is.
If the view plane 10 of FIG. 1 is replaced by the monitor screen, and the corresponding 3-D image produced by a conventional graphic accelerator is represented thereon, the image seen by the human eyes can be depicted as shown in FIG. 2. Once the image appears at the monitor, each eye focuses on the monitor screen and the composite images of views 20, 30 are simultaneously seen by the eyes. Thus, the images presented in the monitor screen cannot be seen with the parallax effect.
In order to separate the left eye's view 20 and the right eye's view 30 in the monitor screen and thus to give the parallax effect, LCD Shutter techniques have been widely used in combination with raster display systems. Such techniques are known in the art as "stereo graphics." FIG. 3 illustrates the LCD Shutter technique. The stereo graphic system includes goggles placed nearby two eyes, and LCD shutters 60 and 70 are provided inside the goggles. In the interlaced monitor screen 40, the left eye's view 20 and the right eye's view 30 are separately presented according to even numbered scan lines 50 and odd numbered scan lines 55. The left shutter 60 and right shutter 70 are operated in synchronization with the even numbered scan plane and odd numbered scan plane, respectively, such that the left LCD shutter 60 is activated during the presentation of the left eye's view 20 while the right LCD shutter 70 is deactivated to shield the right eye's view 30 of the monitor screen.
However, the above LCD shutter system still has limitations in providing a realistic perspective of an object.